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Keywords:

  • boiler safety interlocks;
  • boiler safety instrumented function;
  • boiler Layer of Protection Analysis;
  • boiler safety integrity level

Abstract

Most chemical process plants, petrochemical facilities, and electrical power utilities rely on steam boilers to provide motive power, electricity, and process steam for operations. Safe operation, startup, and shutdown of these boilers require many levels of operational/controls safeguards. The design and selection of safeguards is often guided by the original design of the boiler, equipment manufacturers, internal company standards, and recognized authoritative standards. In the United States, the National Fire Protection Association (NFPA) has promulgated NFPA 85 Boiler and Combustion Systems Hazards Code. This prescriptive code identifies necessary safeguards along with “listing” and “labeling” requirements for some components used as safeguards; however, the Safety Integrity Levels for the multiple safeguard systems have not been quantified. In this article, we use Layer of Protection Analysis methods along with generally accepted probabilities and frequencies of failures to provide a quantitative framework for an owner, operator, or manufacturer to use in designing or evaluating the multiple safeguards necessary for safe steam boiler operation. As part of the analysis, we have provided case studies of boiler failures with a discussion of how additional layers of protection may be either ineffective or missing. © 2012 American Institute of Chemical Engineers Process Saf Prog, 2012